Laser Nanostructured Surface Preparation for Joining Materials

ABSTRACT

A joined article includes a first component having a laser-treated surface portion and a second component having a laser-treated surface portion. An adhesive joins the first component to the second component at the treated surface portion. A method of making a joined article form components and a system for making joined articles are also disclosed.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims priority to U.S. Provisional Patent ApplicationNo. 62/132,296, filed Mar. 12, 2015, titled “LASER NANOSTRUCTUREDPREPARATION FOR JOINING DISSIMILAR MATERIALS,” the entire contents ofwhich are incorporated herein by reference.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH

This invention was made with government support under contract No.DE-ACO5-00OR22725 awarded by the U.S. Department of Energy. Thegovernment has certain rights in this invention.

FIELD OF THE INVENTION

This invention relates generally to the joining of materials withadhesives, surface preparation for joining materials with adhesives, andto materials joined with adhesives.

BACKGROUND OF THE INVENTION

The increasing use of Carbon Fiber Polymer Composite (CFPC) as alightweight material in automotive and aerospace industries requiresmore effective and reliable joining techniques. The surface treatment isa critical step governing the quality of adhesive bonded joints.Traditional surface preparation methods of composite surfaces leave aresin-rich surface layer on the composite, which is susceptible to thenucleation of cracks that may limit its structural integrity. The CFPCsurface also contains chemicals, such as mold releases and contaminants,which often require removal prior to adhesive bonding. Currentstate-of-the art surface preparation for composites is typicallyaccomplished through multiple mechanical/chemical processes, which lackthe speed and repeatability needed for high-throughput manufacturing.They also involve chemicals that often require special handling. Manyadhesive suppliers formulate adhesives to accommodate less than idealsurfaces, at the expense of structural performance.

Aluminum (Al) surfaces contain oxides and lubricant oils that aredetrimental to the adhesive joining. Surface treatments aim at modifyingthe Al surface to attain contaminant removal, wettability with eitherprimer or adhesive, and highly roughened surfaces. Traditional surfacepreparation techniques for Al used in the industry for bonding aluminuminclude grit blasting, solvent wiping followed by abrading (with aScotchBrite® pad), or anodization. The first two are more common,whereas anodization is more commonly seen in aerospace applicationswhere this more expensive and rigorous preparation is necessary to meetstringent specifications. Due to the inherent variability in gritblasting or abrasion techniques, a more controlled process would bedesired.

Surface preparation is one of the main challenges for bonding CFPC withAl, both in consistent quality and productivity. The major roadblocks injoining CFPC and Al is related to the inherent poor mechanical strengthof the resin, as the adhesive does not directly contact the CFPC but theresin rich layer on the CFPC surface. Moreover, the Al surface may betoo smooth to allow an excellent mechanical bonding with the adhesive.Additionally, the surfaces of both materials as noted containcontaminates, which are residual from their forming/molding operations.Aluminum surfaces contain oxides and lubricant oils. Composites containmold releases. Traditional preparation of CFPC surfaces often includechemical removal of mold releases and other handling aids but, evenunder the most ideal scenarios, still leaves a resin rich surface layeron the composite which is susceptible to Mode I fracture sensitivity.

To date, joining CFPCs and metal components, made of aluminum 5000,6000, or 7000 series, titanium, magnesium, and steels is made by simplyoverwrapping the CFPC composite over the aluminum or using speciallyformulated adhesives coupled with extensive surface preparationtechniques. These processes are empirical, employing several steps, suchas labor-intensive surface preparation methods that are incompatiblewith the degree of automation required in automotive applications. Inaddition to the cost and floor space requirements, manual surfacepreparation introduces a significant variability in the overall jointintegrity. The technique is not limited only to aluminum but to anymetal, although Al and CFPC materials are common in the automotive andaerospace industries.

The use of one-beam laser for serial structuring, which can produce onegeometrical feature per laser spot or line raster, has been used in lasttwo decades for CFPC. Niino et al. [H. Niino, M. Nakano, S. Nagano, H.Nitta, K. Yano, A. Yabe, Excimer Laser Ablation of Polymers and CarbonFiber Composites, Journal of Photo polymer Science and Technology, Vol.3 (1990), pp. 53-56.] used a 308 nm XeCI excimer laser to induce surfacemicromodifications onto polymers and carbon fiber composites. The use ofan excimer laser treatment, selective removal of the organic matrixwithout any degradation of fiber reinforcements, was investigated byGalantucci et al. [Galantucci, L M; Gravina, A; Chita, G; Cinquepalmi,M, Surface treatment for adhesive-bonded joints by excimer laser,Composites Part A-Appl. Sci. and Manuf., Vol. 27, pp. 1041-1049, 1996.]and Benard et al. [Benard, Q., Foisa, M., Grisel, M., Laurens, P.,Surface treatment of carbon/epoxy and glass/epoxy composites with anexcimer laser beam, Int. J. of Adhesion and Adhesives, Vol. 26, pp.543-549, 2006] [Benard, Q.; Fois, M.; Grisel, M.; Laurens, P.; Joubert,F., Influence of the Polymer Surface Layer on the Adhesion of PolymerMatrix Composites, J. of Thermoplastic Comp. Mat., Vol. 22, Pages:51-61, 2009]. Warren et al. [Warren, C. D., Paulauskas, F. L., andBowman, R. G., “Laser Ablation Assisted Adhesive Bonding of AutomotiveStructural Composites,” ORNL/CP-102637, ICCM-12, Paris France, Jul. 3-9(1999)] also used a KrF excimer laser to process glass fiber-reinforcedpolymer matrix composites. Significant glass fiber damage was found dueto the ablation process, as the glass fibers acted as a lens focusingthe laser energy to the backside of the fibers and thus producedmicrogrooving of the fiber along the side of the fiber farthest awayfrom the incident direction. Lima et al. [Lima, M. S. F.; Sakamoto, J.M. S.; Simoes, J. G. A.; Riva, R., Laser processing of carbon fiberreinforced polymer composite for optical fiber guidelines, Lasers InManufacturing (LIM 2013), Physics Procedia, Ed. by Emmelmann C; Zaeh MF;Graf T; Schmidt M, Vol. 41, pp. 565-573, 2013] used a 20 W of a Nd:YAGpulsed laser to producing fiber optical guidelines in carbon fiberreinforced polymer (CFRP) composites using laser texturing andmachining. The size of laser-created surface patterns is identical tothe laser spot size. Detrimental microcracks can be propagated into thesubsurface level.

SUMMARY OF THE INVENTION

A joined article includes a first component having a laser-treatedsurface portion and a second component having a laser-treated surfaceportion. An adhesive joins the first component to the second componentat the treated surface portion.

The laser-treated surface portions can include features comprising atleast one selected from the group consisting of depressions, channelsand holes. The features can have a periodicity. The periodicity can bebetween 0.5-50 μm. The periodicity can in one aspect vary by no morethan ±5%.

The laser can be a multiple-beam interference laser, wherein an originallaser beam is split into at least 2 beams which are then refocused overthe same spot on the component surface.

The joined article treated according to the invention can have a tensilestrength that is at least 10% greater than a baseline tensile strengthof an untreated article. The joined article treated according to theinvention can have a ductility that is at least 100% greater than abaseline joint of an untreated article.

The laser-treated surface portion of the first component and thelaser-treated portion of the second component can be dissimilarmaterials. One of the laser-treated surface portions can include acarbon fiber material having carbon fibers embedded in resin. A surfaceportion of the resin can be removed by the laser treatment to exposecarbon fibers. The carbon fibers can have laser-created features formedtherein.

A method of making a joined article from components can include thesteps of treating a surface of a first component with a laser to createa treated surface portion, and treating a surface of a second componentwith a laser to create a treated surface portion. An adhesive is appliedbetween the treated surface portion of the first component and thetreated surface portion of the second component. The treated surfaceportion of the first component is joined to the treated surface portionof the second component.

The laser-treated surface portions comprise spots can include at leastone of depressions, holes and channels. The method spots can have aperiodicity. The periodicity can be between 0.5-50 μm. The periodicitycan vary by no more than ±5%.

The method can include the use of an interference laser. Thelaser-treated surface portion of the first component and thelaser-treated portion of the second component can be dissimilarmaterials.

The laser treating can include between 1-50 laser pulses per spot. Thelaser treating can include laser-component translation with speedsbetween 1 to 500 mm/s. The wavelength of the laser light can be 180-2000nm.

A system for joining articles having at least first and secondcomponents can include an interference laser, wherein an original laserbeam is split into at least 2 beams which are then refocused over thesame spot on the component surface. A support can be provided forrigidly fixturing each of two or more components to be joined, and forregistering the position of the first component and subsequentcomponents relative to the laser. A drive is provided for moving atleast one of the laser and the component supports relative to each otherto apply features to a surface portion of each component.

The system can further include a device for cleaning the surfaces ofeach component prior to adhesive application. The device can be a blowerfor blowing air over the laser processed component surface.

BRIEF DESCRIPTION OF THE DRAWINGS

There are shown in the drawings embodiments that are presently preferredit being understood that the invention is not limited to thearrangements and instrumentalities shown, wherein:

FIG. 1 is a schematic diagram for the optical setup for two-beaminterference.

FIG. 2 is a schematic diagram for the optical setup for three-beaminterference.

FIG. 3 is a schematic diagram for an alternative optical setup for threeor more beams interference.

FIG. 4 is a schematic diagram of the alternating high-power andlow-power profile created by wave interference for two-beaminterference.

FIG. 5 is a schematic diagram of the alternating high-power andlow-power profile created by wave interference for three or more beamsinterference.

FIG. 6 is a schematic diagram of a laser spot profile for a rasteringmode with 5 mm/s rastering speed.

FIG. 7 is a schematic diagram of a laser spot profile for a rasteringmode with 10 mm/s rastering speed.

FIG. 8 is a schematic diagram of a laser spot profile for a spot-by-spotmode with a beam size of 4 mm covering an area of 25×25 mm.

FIG. 9 is a schematic diagram of a laser spot profile for a spot-by-spotmode with a beam size of 6 mm covering an area of 25×25 mm.

FIG. 10 is a schematic diagram illustrating the effect of the inventionon a carbon fiber polymer composite.

FIG. 11 is a schematic diagram of the adhesive-resin interface for acarbon fiber polymer composite without laser structuring.

FIG. 12 is a schematic diagram of the adhesive-resin interface for acarbon fiber polymer composite with laser structuring at 2 shots perspot.

FIGS. 13 A-D are schematic diagrams illustrating the laser structuringof carbon fibers where A) is a perspective view; B) is a side view; C)is a top view; and D) is a vertical cross section through a verticalcarbon fiber.

FIG. 14 is a schematic diagram of the expected surface morphologyinduced through the laser-structuring of Al.

FIGS. 15 A-C are schematic diagrams of surface profiles of A)unprocessed aluminum; B) aluminum processed using a 2 beam laserinterference; and C) a cross section of the aluminum taken along lineA-A of FIG. 15 B).

FIG. 16 is a schematic diagram of a system for joining articlesaccording to the invention.

FIG. 17 is a schematic diagram of a joined article according to theinvention.

FIG. 18 is a plot of shear lap stress (psi) vs. displacement (in.) foran unstructured joint, a spot-by-spot laser-interference structure, anda laser-interference raster structure.

FIG. 19 is a plot of shear lap strength (psi) for differing joint types(baseline, 2B-raster, 3B-raster and 3C-spot) for a first adhesive.

FIG. 20 is a plot of shear lap strength (psi) for differing joint types(baseline, 2B-raster, 2B-spot(6) and 2B-spot(4)) for a second adhesive.

FIG. 21 is a plot of shear lap strength (psi) for differing joint types(baseline, 2B-raster, and 2B-spot) for a third adhesive.

FIG. 22 is a plot of bond length (mm) for differing joint types(baseline, 3C-spot, 2B-raster and 3B-raster) for a first adhesive.

FIG. 23 is a plot of bond length (mm) for differing joint types(baseline, 2B-raster, 2B-spot(6) and 2B-spot(4)) for a second adhesive.

FIG. 24 is a plot of bond length (mm) for differing joint types(baseline, 2B-raster, and 2B-spot) for a third adhesive.

DETAILED DESCRIPTION OF THE INVENTION

A joined article includes a first component having a laser-treatedsurface portion and a second component having a laser-treated surfaceportion. An adhesive joins the first component to the second componentat the treated surface portion. The laser-treated surface portions caninclude features comprising depressions, channels or holes. The featurescan have a periodicity. The laser-treated surface portion of the firstcomponent and the laser-treated portion of the second component can bedissimilar materials.

The laser can be a multiple-beam interference laser, wherein an originallaser beam is split into at least 2 beams, which are then refocused overthe same spot on the component surface. The laser beam can be split into3 or more beams.

The laser-treated surface portions can include features or spotscomprising depressions. The spots can have a periodicity. Theperiodicity can be well defined by the wavelength (A) and the angle (a)between two beams:

$d = \frac{\lambda}{2\mspace{11mu} \sin \mspace{11mu} \left( {\alpha/2} \right)}$

The periodicity can be between 0.5-50 μm. The periodicity can vary by nomore than ±5%. The laser patterns can be dot-, line-, and ring shaped.

The laser treating can include between 1-50 laser pulses per spot. Thelaser treating can include laser-component translation or rastering withspeeds between 1 to 500 mm/s. The wavelength of the laser light can be180-2000 nm. The pulse duration can be between 10fs-10 ns. The averagepower of the laser can be between 0.1-3,000 W.

For example, with only 10 ns the laser pulse duration is very short,creating an extremely high peak power above 100 MW, resulting in greaterthan 10¹²K/s heating rates on a nickel/aluminum composite structure witha photothermal response. Materials showing a photochemical responseablate with minor temperature increase. Laser intensity, wavelength andpulse patterns can be tuned to achieve the optimum surface texture basedon crack arrest criteria for preventing interfacial crack growth alongthe adhesive/aluminum interface.

The invention is useful for joining metals, carbonaceous materials,polymeric materials, and ceramics. Examples of suitable metals includealuminum, titanium, magnesium, steels, and alloys thereof. Examples ofcarbonaceous materials include CFPCs, as well as other compoundmaterials where a laser ablatable first material such as a resin hasembedded therein a reinforcing or other material-property modifyingsecond material that is resistant to laser ablation, such as carbonfiber and glass fiber. Examples of suitable ceramic materials includesilicon carbide, hydroxyapatite, and alumina.

The laser-treated surface portion of the first component and thelaser-treated portion of the second component can be dissimilarmaterials. One of the laser-treated surface portions can include a CFPCmaterial having carbon fibers embedded in resin. A surface portion ofthe resin can be removed by the laser treatment. The laser treatment canalso produce laser-created features in the carbon fibers.

The CFPC surface can be prepared by selectively ablating the resin richsurface layer and also ablating, to a pre-determined depth, the resin inthe top fiber layers of the composite. The ablation depth can be between3-50 μm. Laser intensity and wavelength can be tuned to remove resinwithout damaging the fibers. Thus, the untreated sharp adhesive/resinrich interface of the CFPC is replaced by a rough, fiber-reinforcedinterface through which the adhesive would bond more effectively.Additionally, the method of the invention will clean contaminants suchas mold release agents, lubricant oils and oxides from the surface.After the laser scanning of contacting surfaces, CFPC composites wouldbe joined to the opposing surface of the second component using anadhesive, interlocking the materials to form a joint between the CFPC ofthe first component and other material, for example aluminum, of thesecond component.

The adhesive can be any suitable adhesive. Suitable adhesives includethose based on epoxy, polyurethane, and acrylic, which are commonly usedin the industry.

The joined article treated according to the invention can have: (a) atensile strength that is at least 10% greater than a baseline tensilestrength of an untreated article, and/or (b) have an 100% increase inductility, i.e., a 100% increase in the displacement at failure duringshear-lap testing.

FIG. 1 is a schematic depiction of three alternative optical setups forthe two-beam interference. The optical components are: MS—mechanicalshutter, BS—beam splitter, M—mirror, and L—lens. FIG. 2 is a schematicdepiction of the optical setup for the multiple-beam interference.

FIG. 3 is a schematic depiction of the optical setup for a femtosecondlaser in which the interference patterns were produced using adiffractive beam splitter (DBS) and confocal imaging system with twoconvex lenses.

FIG. 4 illustrates the alternating, high-power and low-power profilecreated by 2-beam wave interference, which yields localized melting andsurface structuring. FIG. 5 illustrates the alternating, high-power andlow-power profile created by multiple-beam wave interference (more than3 beams), which yields localized melting and surface structuring.

FIGS. 6-9 are schematic illustrations of the laser spots for a 25×25 mmcoverage area. FIG. 6 is a depiction of features or spots created by a 5mm/s rastering speed. FIG. 7 is a depiction of the feature pattern for a10 mm/s rastering speed. The overlap distance of rows in FIGS. 6-7 is 1mm. FIG. 8 is a depiction of the feature pattern created by the laser inspot-by-spot mode with a beam size of 4 mm. FIG. 9 is a depiction of thefeature pattern created by the laser in spot-by-spot mode with a beamsize of 6 mm.

The optical micrographs of laser ablated CFPC specimens show that carbonfibers are directly exposed on both top surface and on side surfaces,creating an improved bonding surface for the adhesive. The laserstructuring of CFPC addresses the prior problems related to CFPC joiningwith Al in which adhesive does not directly contact the CFPC but insteadthe resin rich layer on the CFPC and the inherent poor mechanicalstrength of that resin. The resin rich surface layer on the composite isalso susceptible to Mode I fracture (delamination) sensitivity as theadhesive/resin interface relies only upon chemical bonding and is planarin nature. FIG. 10 illustrates the expected effects due tolaser-structuring of CFPC, in which the resin rich near surface isremoved along with mold release agents and surface contaminants toexpose the carbon fibers to the adhesive. FIG. 11 is a rendering of theadhesive-resin interface of a baseline joint without laser structuring,and FIG. 12 illustrates the adhesive-resin interface of a joint in whichthe CFPC was laser-structured with 2 shots per spot. The adhesivedirectly contacts and engages the roughened surface created by theexposed carbon fibers.

FIG. 13 illustrates the laser structuring of the carbon fibersthemselves. FIG. 13A illustrates a fiber arrangement in which the carbonfibers at the surface are structured and those behind them are notstructured. FIG. 13B is a side view illustrating the depth of thefeatures relative to the fibers. FIG. 13C is a top view of the carbonfiber surface that is exposed to the adhesive. FIG. 13D is cross-sectionthrough a carbon fiber showing the periodic structuring. The depth ofthe grooves can be varied by increasing the laser power, and theperiodicity can be changed by varying the angles between the beams.

FIG. 14 is a schematic depiction of the expected surfacemorphology/topology induced through laser-structuring of Al. The shapeincluding the aspect ratio, the periodicity and the distribution of thefeatures can vary.

FIG. 15 is a schematic depiction of 3-D surface profiles of an aluminumsurface. FIG. 15A is a depiction of an as-received unprocessed aluminumsurface. FIG. 15B and FIG. 15C are schematic depictions of a laserstructured aluminum surface using a 2 beam laser interference techniquewith 10 pulses.

A system for joining articles having at least first and secondcomponents is shown in FIG. 16. The system can include an interferencelaser 30, wherein an original laser beam is split into at least 2 beams,which are then refocused over the same spot on the component surface 34.A support 38 is provided for rigidly fixturing each of two or morecomponents to be joined, and for registering the position of the firstcomponent and subsequent components relative to the laser 30. A drive 42is provided for moving at least one of the laser 30 and the componentsupport 38 relative to each other to apply features to a surface portionof each component. The system can further include a device for cleaningthe surfaces of each component prior to adhesive application. The devicecan be a blower 44 for blowing air over the laser processed componentsurface.

A joined article 50 according to the invention is shown in FIG. 17. Thearticle 50 includes a first component 54 and a second component 58. Thefirst component 54 can be a CFPC in which a surface portion has beenremoved to expose carbon fibers 62. The carbon fibers 62 that extendfrom the ablated resin surface 64 can have laser-structured features 66formed therein. Spaces 68 between the exposed carbon fibers 62 alsoprovide features for engaging the adhesive. The second component 58 canhave features 70. An adhesive 74 is interposed between the firstcomponent 54 and the second component 58 and contacts the carbon fibers62 and feature bordering the spaces 68, and also contacts the secondcomponent 58 and features 70.

A method of making a joined article from components can include the stepof treating a surface of a first component with a laser to create atreated surface portion. A surface of a second component can be treatedwith a laser to create a treated surface portion. An adhesive can beapplied between the treated surface portion of the first component andthe treated surface portion of the second component, and the treatedsurface portion of the first component can be joined to the treatedsurface portion of the second component.

Experimental Setup

Baseline joints were made without involving laser structuring by usingAl and CFPC samples that were abraded using a ScotchBrite® pad andultrasonically cleaned using ethanol. The baseline joints were used toassess the improvements in the joint strength for the joints producedwith the laser-structured Al and CFPC. Both CFPC and Al specimens werelaser-structured using the interference technique in as-receivedcondition, without any additional surface preparation steps. Prior tojoining, the laser-structured samples were not cleaned with anysolvents. Two types of laser structuring were employed: (1) rastering,in which the laser beam was translated over the sample surface while thelaser was on, and (2) spot-by-spot, in which the laser beam was heldover each spot for a certain amount of time in order to allow multiplelaser shots over the same area.

A 10 Hz Q-switched Nd:YAG laser (Quanta-Ray PRO 230, Spectra Physics)was used to process specimens. The pulse width was 10 ns and the beamdiameter was varied from 2 to 8 mm. The fundamental emission with thewavelength of 1064 nm was transformed to 355 nm and 266 nm usingnon-linear crystals. The maximum laser energy per pulse was 0.35 J at355 nm and 0.04 J at 266 nm. The number of pulses is selected by amechanical shutter. The primary laser beam was split into two beams andguided with mirrors onto the specimen surface. The laser interferencepower profile was created by guiding those beams to the sample surfaceby overlapping each other with defined angles to each other. Thecoherent beams create an interference pattern instead of adding theirintensity. This allows a microscopic modulation and creates a lightpattern without any loss of energy during the interference process.

In some experiments, two identical focal lenses were used in each pathof the splitted beam to focus laser beams from 8 mm to smaller sizes,hence increasing the laser pulse fluences. For the laser structuring ofAl and CFPC nano-second lasers, the optimum pulse fluence of the lasercan be 0.2 to 3 J/cm². Periodic lines structures were formed on thesurface by laser interference. The specimen was fixed on a translationstage capable of moving in horizontal and vertical directions. A LabVIEWbased computer program was used to automatically control the location ofthe translation stage and the shutter opening time. During theexperiments, the specimen attached to the translation stage was firstlymoved to a predefined coordinate origin, followed by a shutter openingto transmit a certain number of laser pulses. For spot-by-spotstructuring, the specimen was moved to the next position followed byanother shutter opening. By repeating this procedure, an entire surfacearea of the specimen was processed. For the rastering mode, the shutterwas open while the specimen was translated over the laser spot and laserfired shots with a 10 Hz frequency. After a horizontal line wascompleted, the shutter was closed and the specimen was moved to thestart of the next line.

A WYKO 9100 surface profilometer was used to obtain surface roughnessdata for the as-received CFPC. WYKO surface profilometer systems arenon-contact optical profilers that use two methods to measure a widerange of surface topographical features. Phase-shifting interferometrymode allows the measurement of smooth surfaces and small steps, whilevertical scanning interferometry mode allows the measurement of roughsurfaces and steps up to several mm high. The surface profile shown ofthe as-received CFPC exhibited some grooves on its surface,approximately 9 μm deep, which may be generated from a previousprocessing step such as rolling. The average roughness, or arithmeticalmean deviation of the roughness profile, Ra, root-mean-square deviationof the roughness profile, Rq, and maximum height of the roughnessprofile, Rt, were estimated.

The examples utilize Al 5182 as one component and as the other componentcarbon fiber polymer composites (CFPC) made from Prepreg-T83 resin(epoxy) and T700S Carbon Fiber, supplied as 5 ply thick, 0/90° plaquesfrom Clearwater Composites Inc. (Duluth Mich.). The dimensions of the Alsamples were 1.5 mm thick, 100 mm width, and 300 mm long. The dimensionsof the CFPC samples were 1.08 mm thick, 100 mm width, and 300 mm long.The diameter of one carbon fiber (CF) was approximately 6.7 μm.

The adhesives that were used included DP460—an epoxy, DP620—apolyurethane, and DP810—a low-odor acrylic, all from 3M (St. PaulMinn.).

The surface roughness increased from 226 nm (as-received) to 392 nm forthe laser interference structured surface of Al 5182 with 10 pulses/spot(λ=355 nm, pulse fluence of 1.2 J/cm²), as shown in Table 1. Thefollowing data was obtained with an optical surface profilometer:arithmetical-mean deviation of the roughness profile (Ra),root-mean-square deviation of the roughness profile (Rq), and totalheight of the roughness profile (Rt). The laser-interference structuringincreased the surface area that would be in contact with the adhesive.

TABLE 1 Condition Ra [μm] Rq [μm] Rt [μm] Untreated 0.226 0.286 3.21Laser treated 0.391 0.493 4.68

The results from mechanical testing on the lap shear strength are shownin FIG. 18. Shear lap stress data was obtained for Al-CFPC joints for abaseline joint (24.8×26.65), a spot-by-spot laser-interferencestructured Al and CFPC (24.87×25.18), and laser-interference raster ofjoint surfaces (25.08×26.45). The width and the length of the actualjoined area are indicated in parenthesis as (W×L) in mm.Laser-structured joints are more ductile, indicating an enhancedadhesion of adhesive to both Al and CFPC. The displacement at failureincreasing from 0.145 in for the baseline joint to more than 0.26 in forthe laser-structured joints. Laser structured joints can absorbapproximately 50% more energy than baseline joints.

There is shown in FIGS. 19-21 the single-lap shear strength results forminimum, mean, and maximum values for baseline and laser-interferencestructured surfaces for both CFPC and Al for the DP810 adhesive (FIG.19), the DP460NS adhesive (FIG. 20), and the DP620NS adhesive (FIG. 21).

The effect of laser structuring for different adhesives was assessedwith a total of sixty Al and carbon fiber polymer composite (CFPC)joints. The joints were bonded using the three adhesives, as follows: 24joints for DP810, 18 joints for DP460, and 18 joints for DP620 (Table2). Six joint specimens were made for each joint type to assess theeffect of adhesive for laser structured surface preparation overconventional surface preparation. The conditions for laser rastering andlaser spot-by-spot processing modes were selected based on a sensitivitystudy for DP810 adhesive. Six specimens were used for each joint type.Thus, the single-lap shear increase was not due to the variation in thebond length but solely due to laser structuring.

TABLE 2 Adhesive Joint Type Preparation of CFPC Preparation of Al DP810Baseline abraded and ethanol abraded and ethanol cleaned cleaned DP460NSbaseline abraded and ethanol abraded and ethanol cleaned cleaned DP620NSbaseline abraded and ethanol abraded and ethanol cleaned cleaned DP8102B-raster Laser raster #2 Laser raster B DP810 3B-raster Laser raster #3Laser raster B DP810 3C-spot Laser spot-by-spot #3 Laser spot-by-spot CDP460NS 2B-raster Laser raster #2 Laser raster B DP460NS 2B-spot Laserspot-by-spot #2 Laser spot-by-spot B DP620NS 2B-raster Laser raster #2Laser raster B DP620NS 2B-spot Laser spot-by-spot #2 Laser spot-by-spotB

Raster #2 indicates 5 mm/s @ 3.5 W, spot size 4 mm, and overlap betweensuccessive rows of 1 mm. Raster #3 indicates 10 mm/s @ 3.5 W, spot size4 mm, and overlap between successive rows of 1 mm. Raster B indicates 5mm/s @ 3.5 W, spot size 4 mm, and overlap between successive rows of 1mm. Spot-by-spot #2 indicates 4 shots/spot @ 3.5 W, spot size 6 mm, andoverlap between successive rows of 1 mm. Spot-by-spot B indicates 4shots/spot @ 2.86 W, spot size 6 mm, and overlap between successive rowsof 1 mm. Spot-by-spot C indicates 2 shots/spot @ 2.86 W, spot size 6 mm,and overlap between successive rows of 1 mm.

The bond length data shown in FIGS. 22-24 illustrate the minimum, mean,and maximum for baseline and laser-interference structured surfaces forboth CFPC and Al for DP810 adhesive (FIG. 22), the DP460NS adhesive(FIG. 23), and the DP620NS adhesive (FIG. 24).

Table 3 shows the increase in mean shear-lap strength (from FIGS. 19,20, and 21) in percentage for the laser-structured joint components withrespect with their corresponding baselines. The results show that theshear-lap strength of Al-CFPC joints has increased by 12-35% usinglaser-interference structuring.

% increase by % increase by Adhesive laser-raster laser spot-by-spot 81012.7-14.8 16.3 460NS 12.8 8.2-12.8 620NS 35.3 25.4

Ranges: throughout this disclosure, various aspects of the invention canbe presented in a range format. It should be understood that thedescription in the range format is merely for convenience and brevityand should not be construed as an inflexible limitation on the scope ofthe invention. Accordingly, the description of a range should beconsidered to have specifically disclosed all the possible subranges aswell as individual numerical values within that range. For example,description of a range such as from 1 to 6 should be considered to havespecifically disclosed subranges such as from 1 to 3, from 1 to 4, from1 to 5, from 2 to 4, from 2 to 6, from 3 to 6 etc., as well asindividual numbers within that range for example, 1, 2, 2.7, 3, 4, 5,5.3 and 6. This applies regardless of the bread of the range.

This invention can be embodied in other forms without departing from thespirit or essential attributes thereof, and accordingly, referenceshould be had to the following claims to determine the scope of theinvention.

We claim:
 1. A joined article, comprising: a first component having alaser-treated surface portion; a second component having a laser-treatedsurface portion; an adhesive joining the first component to the secondcomponent at the treated surface portion.
 2. The joined article of claim1, wherein the laser-treated surface portions comprise featurescomprising at least one selected from the group consisting ofdepressions, channels and holes.
 3. The joined article of claim 2,wherein the features have a periodicity.
 4. The joined article of claim3, wherein the periodicity is between 0.5-50 μm.
 5. The joined articleof claim 3, wherein the periodicity varies by no more than ±5%.
 6. Thejoined article of claim 1, wherein the laser is a multiple-beaminterference laser, wherein an original laser beam is split into atleast 2 beams which are then refocused over the same spot on thecomponent surface.
 7. The joined article of claim 1, wherein the joinedarticle treated according to the invention has a tensile strength thatis at least 10% greater than a baseline tensile strength of an untreatedarticle.
 8. The joined article of claim 1, wherein the joined articletreated according to the invention has a ductility that is at least 100%greater than a baseline joint of an untreated article.
 9. The joinedarticle of claim 1, wherein the laser-treated surface portion of thefirst component and the laser-treated portion of the second componentare dissimilar materials.
 10. The joined article of claim 1, wherein oneof the laser-treated surface portions comprises a carbon fiber materialhaving carbon fibers embedded in resin, and wherein a surface portion ofthe resin has been removed by the laser treatment.
 11. The joinedarticle of claim 10, wherein the carbon fibers comprise laser-createdfeatures.
 12. A method of making a joined article from components,comprising the steps of: treating a surface of a first component with alaser to create a treated surface portion; treating a surface of asecond component with a laser to create a treated surface portion;applying an adhesive between the treated surface portion of the firstcomponent and the treated surface portion of the second component, andjoining the treated surface portion of the first component to thetreated surface portion of the second component.
 13. The method of claim12, wherein the laser-treated surface portions comprise spots comprisingat least one selected from the group consisting of depressions, holesand channels.
 14. The method of claim 13, wherein the spots have aperiodicity.
 15. The method of claim 14, wherein the periodicity isbetween 0.5-50 μm.
 16. The method of claim 14, wherein the periodicityvaries by no more than ±5%.
 17. The method of claim 12, wherein thelaser is an interference laser.
 18. The method of claim 12, wherein thelaser-treated surface portion of the first component and thelaser-treated portion of the second component are dissimilar materials19. The method of claim 12, wherein the laser treating comprises between1-50 laser pulses per spot.
 20. The method of claim 12, wherein thelaser treating comprises laser-component translation with speeds between1 to 500 mm/s.
 21. The method of claim 12, wherein the wavelength of thelaser light is 180-2000 nm.
 22. A system for joining articles comprisingat least first and second components, comprising: an interference laser,wherein an original laser beam is split into at least 2 beams which arethen refocused over the same spot on the component surface; a supportfor rigidly fixturing each of two or more components to be joined, andfor registering the position of the first component and subsequentcomponents relative to the laser; a drive for moving at least one of thelaser and the component supports relative to each other to applyfeatures to a surface portion of each component.
 23. The system of claim22, further comprising a device for cleaning the surfaces of eachcomponent prior to adhesive application.
 24. The system of claim 22,wherein the device is a blower for blowing air over the laser processedcomponent surface.